Aggregate OD data between polygon geometries

Aggregate OD data between polygon geometries

od_aggregate(flow, zones, aggzones, aggzone_points = NULL,
  cols = FALSE, aggcols = FALSE, FUN = sum,
  prop_by_area = ifelse(identical(FUN, mean) == FALSE, TRUE, FALSE),
  digits = getOption("digits"))

Arguments

flow	A data frame representing the flow between two points or zones. The first two columns of this data frame should correspond to the first column of the data in the zones. Thus in cents(), the first column is geo_code. This corresponds to the first two columns of flow().
zones	A SpatialPolygonsDataFrame or SpatialPointsDataFrame representing the original centroids or boundaries of the travel flow data. Note that in the case of a SpatialPointsDataFrame, the entirety of the flow will be allocated to the polygon in which the point is located rather than being distributed by area.
aggzones	A SpatialPolygonsDataFrame containing the new boundaries to aggregate to.
aggzone_points	Points representing origins of OD flows (typically population-weighted centroids)
cols	A character vector containing the names of columns on which to apply FUN. By default, all numeric columns are aggregated.
aggcols	A character vector containing the names of columns in aggzones to retain in the aggregated data.frame. By default, only the first column is retained. These columns are renamed with a prefix of "o_" and "d_".
FUN	Function to use on aggregation. Default is sum.
prop_by_area	Boolean value indicating if the values should be proportionally adjusted based on area. Default is TRUE unless FUN = mean.
digits	The number of digits to use when proportionally adjusting values based on area. Default is the value of getOption("digits").

Value

data.frame containing the aggregated od flows.

Details

Origin-destination ('OD') flow data is often provided in the form of 1 line per flow with zone codes of origin and destination centroids. This function aggregates OD flows between polygon geometries allocating the original flows to larger zones based on area.

Examples

zones$quadrant <- c(1, 2, 1, 4, 5, 6, 7, 1)
aggzones <- rgeos::gUnaryUnion(zones, id = zones@data$quadrant)
aggzones <- sp::SpatialPolygonsDataFrame(aggzones, data.frame(region = c(1:6)), match.ID = FALSE)
sp::proj4string(aggzones) <- sp::proj4string(zones)
aggzones_sf <- sf::st_as_sf(aggzones)
aggzones_sf <- sf::st_set_crs(aggzones_sf, sf::st_crs(zones_sf))
od_agg <- od_aggregate(flow, zones_sf, aggzones_sf)
#> Warning: st_centroid assumes attributes are constant over geometries of x
#> Warning: st_centroid does not give correct centroids for longitude/latitude data
#> Warning: st_centroid assumes attributes are constant over geometries of x
#> Warning: st_centroid does not give correct centroids for longitude/latitude data
#> although coordinates are longitude/latitude, st_intersects assumes that they are planar
#> Joining, by = "Area.of.residence"
#> Warning: Column `Area.of.residence` joining character vector and factor, coercing into character vector
#> Joining, by = "Area.of.workplace"
#> Warning: Column `Area.of.workplace` joining character vector and factor, coercing into character vector
colSums(od_agg[3:9]) == colSums(flow[3:9])
#>                                  All          Work.mainly.at.or.from.home 
#>                                 TRUE                                 TRUE 
#> Underground..metro..light.rail..tram                                Train 
#>                                 TRUE                                 TRUE 
#>                Bus..minibus.or.coach                                 Taxi 
#>                                 TRUE                                 TRUE 
#>         Motorcycle..scooter.or.moped 
#>                                 TRUE 
od_sf_agg <- od2line(od_agg, aggzones_sf)
#> Warning: st_centroid assumes attributes are constant over geometries of x
#> Warning: st_centroid does not give correct centroids for longitude/latitude data
plot(flowlines, lwd = flowlines$Bicycle)
plot(od_sf_agg$geometry, lwd = od_sf_agg$Bicycle, add = TRUE, col = "red")